Quantifying marine redox across the Triassic Jurassic mass extinction

As anthropogenic carbon emissions continue to alter global temperatures and weathering rates, studies of environmental analogues attempt to predict the pattern of subsequent marine redox changes as well as the vulnerability of marine ecosystems. One such analogue may take the form of the Triassic–Jurassic boundary interval (~201 Ma) which has been closely associated with widespread marine de-oxygenation and marine mass extinction. However, relatively little is understood about the initiation and spatio-temporal progression of marine redox change during this interval, as well as the vulnerability of different sub-environments and/or biota to redox changes. This thesis has used the elemental and isotopic compositions of marine sediments to reconstruct marine redox change on the Tethyan shelf, during the Triassic–Jurassic boundary interval, in a bid to further understand the complex nature of marine de-oxygenation during an interval of global environmental change. The work undertaken within this thesis demonstrates that Triassic–Jurassic marine de-oxygenation on the Tethyan shelf, and in the open ocean, coincided with intervals of marine extinction, particularly amongst benthic organisms, potentially suggesting causality. This thesis reveals that marine redox change on the Tethyan shelf was pulsed in nature and was largely preceded by open ocean de-oxygenation, meaning that marine redox change may have progressed from the open ocean to marginal marine environments. Mo isotope data presented here reveals that sulfidic conditions covered no more than 0.05–0.1% of the Late Triassic seafloor and were likely geographically restricted to marginal marine environments. However, on the marginal marine Tethyan shelf sulfidic conditions were limited spatially in comparison to sedimentary porewater and bottom water de-oxygenation, which was more widespread. Late Triassic marine redox change is poorly correlated to changes in detrital input, weathering, grain size and hydrography on the Tethyan shelf potentially suggesting marine redox change being driven by regional nutrient changes, stratification, ocean warming or changes to ocean circulation. The work undertaken within this thesis therefore advances understanding of redox evolution during the Triassic–Jurassic boundary interval as well as its potential role in marine extinctions during the ETME.